Control column shakers or stick shakers for fixed-wing aircraft are well known for unmistakably relaying advance warning of an impending stall. Such shakers have been adapted for use on high performance and other aircraft. They are typically mounted on the aircraft's control column. These units electrically provide a high amplitude, low frequency buffet signal to a pilot. Such signals cannot be confused with other warnings and provide a pilot with a reliable stall warning. Control column shakers of various designs are presently manufactured and sold by Safe Flight Instrument Corporation of White Plains, N.Y., the assignee on the present invention.
The uses of control column shakers in rotary wing aircraft have also been disclosed, as in U.S. Pat. No. 4,115,755 to Cotton. As disclosed therein, an alarm, such as a shaking of the collective pitch control lever of a helicopter, is used as an indication that the actual acceleration exceeds the permissible acceleration. As disclosed by the Cotton patent, the structural envelope of the aircraft, as defined by weight, air speed, rotor rpm, air density and collective stick position, is used as an indication of permissible loading of a helicopter rotor. Cotton also teaches the use of a gross measure of the aircraft weight, density of the air, air speed, the collective pitch and rotor speed of the aircraft as indices of a table look-up to determine the maximum permissible aircraft acceleration under such flight conditions which is then compared against the actual aircraft acceleration to determine when the aircraft is maneuvered close to a loading which exceeds a structural envelope. cl SUMMARY OF THE INVENTION
It is presently believed that there is a significant demand for an improved collective control shaker in accordance with the present invention. It is believed that there is a significant demand for a two-stage tactile warning system which alerts a pilot that he/she is approaching a dangerous condition and then warns the pilot when immediate corrective action should be taken. With this approach, the pilot can fly the aircraft close to its critical limitations and at the same time take corrective action when it becomes necessary.
The collective control shaker in accordance with the present invention provides a first sensory warning when the aircraft is close to a relatively critical stage with respect to any one of a number of flight conditions. For example, as the aircraft approaches a dangerous condition, the shaker vibrates the collective control at a first frequency or amplitude to alert the pilot to either push the collective in a downward direction, or to at least be prepared to do so. Then if any one of a number of flight characteristics becomes more critical, the shaker produces a more violent shaking to provide a vigorous sensory signal to indicate the need for immediate action.
The tactile warning system in accordance with the present invention enables a pilot to fly a helicopter safely at maximum loading within its structural envelope. The system provides an alert signal, such as a vibration of the collective control at a first frequency or amplitude when any one of several operating parameters reaches a first preselected level. The system then provides a more noticeable signal, such as a violent shaking, which overrides the first signal when any one of several parameters becomes critical. The operating parameters may include engine torque, exhaust gas temperature, rotor speed, turbine output shaft speed, turbine inlet temperature, etc.
In addition, the tactile warning system in accordance with the present invention is durable, reliable and can be manufactured, installed and serviced at a competitive cost.
In essence, the present invention contemplates a two-stage alarm for a rotary wing aircraft, such as a helicopter. The alarm operates on a collective control arm of the type used in the control of helicopters. A moveable mass or weight is operatively connected to the collective control arm as, for example, by being mounted thereon or bolted thereto. The moveable weight may be of a reciprocating type or a rotary driven mass which is mounted eccentrically, i.e. for rotation about an axis which is spaced from the center of gravity of the weight. In the latter case, means such as a D.C. motor spins the weight rapidly about the axis at a first speed to produce a shaking action to the collective control arm as a warning of an approaching danger. Means are also provided for moving the weight more rapidly, as for example by a higher voltage, to produce a much more noticeable action at a second frequency, or at an increased amplitude as a warning of a more imminent or serious condition which requires immediate action.
A tactile warning system in accordance with a preferred embodiment of the invention includes a collective control arm and a shaker mechanism operatively connected to the collective control arm. The shaker mechanism may be mounted on, bolted or otherwise fixed to the collective control arm. The system also includes means for sensing a first pre-selected flight condition which is indicative of an approaching danger and a second pre-selected flight condition which is indicative of a more imminent danger and means for producing first and second signals in response to the sensed conditions. The shaker mechanism includes means for producing a first level of sensory perception in response to the first of the signals and a second level of sensory perception which overrides the first level of sensory perception in response to the second signal. In this way, a pilot is warned that he/she is operating a helicopter near a dangerous condition and then given a second warning when the condition becomes critical. The invention will now be described in connection with the following drawings wherein like reference numerals have been used to indicate like parts.